It is known in prior art brake booster to provide an accumulator to a hydraulic brake booster so that when the power source fails stored pressurized fluid in the accumulator is available to assist in actuating braking. For example, if the fan belt on a motor vehicle breaks, the power steering pump is disabled so that no source of fluid pressure is available to actuate braking unless a secondary pressure source is provided. Consequently, prior art brake boosters provide an accumulator which is communicated with the brake booster pressure chamber when the pressure source is disabled to actuate braking.
In view of the decreasing size of most motor vehicles in order to compensate for fuel consumption, engine compartments are also diminishing. With less space for mounting a hydraulic brake booster, it is advantageous to provide a compact hydraulic brake booster for easier installation and maintenance. However, the compact booster must include a secondary pressure source for assisting brake application when the main pressure source is rendered inoperative.